handoff: P1.3.3 challenge canon-parity refactor (0.21.0)

[klappy]

Fresh-session handoff at session close after P1.3.2 shipped end-to-end (see klappy://odd/ledger/2026-04-20-p1-3-2-gate-canary-landed).

This is the legitimate cross-session handoff, not the same-session anti-pattern the P1.3.2 ledger just named. Receiving session is a different conversation / context window / agent start. Tonight's session wrote this at close, not mid-stream.

Scope — exactly three items, ~45-75 min to prod

1. Migrate evaluatePrerequisiteCheck from regex to stemmed set intersection. D5 from P1.3.2 (split-by-fit: prereq evaluation is independent gap-or-not, not ranked; set intersection is the fit-to-problem matcher; avoids BM25 IDF-negative pathology). L2294 definition, L2129 call site, parsers around L413-435 and L709+.

2. Remove cachedChallengeTypeIndex, rebuild inline per D9. Microsecond derivation over 6-9-type corpus; caching adds plumbing without throughput benefit. L163-164, L634-651, L1518-1519, L2028. Parse-product caches stay (cachedChallengeTypes, cachedBasePrerequisites, cachedNormativeVocabulary, cachedStakesCalibration).

3. Graduate cache-fetches-and-parses to canon. canon/principles/cache-fetches-and-parses.md. Third deciding-argument recurrence after P1.3.2's D9 — graduation test satisfied. Canon-first: this doc ships before the code PR.

Ship as 0.21.0

No envelope changes. No new governance files. No multi-phase sequencing. Smaller than P1.3.2 because the design work is reused.

Out of scope (named explicitly to prevent scope creep)

• encode's triggerRegex paragraph classification — different tool, different code path, separate PR
• global cachedBM25Index — may have a size-threshold answer; not a challenge concern
• other carry-forward O-opens P2-P6

Thin prompt for next session

Included in the handoff body. Points the next session at the handoff URI, the P1.3.2 ledger for D5/D9 rationale, and the vodka-architecture canon doc for principle-doc structure.

Refs

• P1.3.2 ledger: klappy://odd/ledger/2026-04-20-p1-3-2-gate-canary-landed
• Prior feat PRs: feat(gate): governance-driven BM25 + set intersection + envelope (0.20.0) oddkit#118 (260492c), odd: P1.3.1 closeout ledger + P1.3.2 gate forward handoff #119 (1308245)
• Prior canon PRs: odd/gate: canon governance docs for P1.3.2 gate vodka refactor (Phase 1) #120 handoff: P1.3.2 Phase 2 forward handoff #121 odd/gate/transitions: add inflected forms for geminating verbs #122 odd: P1.3.2 closeout ledger + supersede obsolete handoffs #123

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Note

Low Risk
Documentation-only change adding a session handoff; no runtime, data, or security behavior is modified.

Overview
Adds a new handoff doc (odd/handoffs/2026-04-20-p1-3-3-challenge-revisit.md) that scopes and line-references the next planned P1.3.3 work: switching challenge prerequisite evaluation from regex to stemmed set intersection (D5), removing cachedChallengeTypeIndex in favor of per-request index rebuilds (D9), and drafting a new canon principle cache-fetches-and-parses to formalize the caching rule.

No code, tests, or production behavior changes are included in this PR; it’s a forward-looking execution plan and checklist for the next session/release (0.21.0).

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